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Intake temp vs coolant temp.

chicagochuck

chicagochuck

New member
2001 gt 97,000

I have been having hesitation problems off and on at certain speeds. it tends to happen on warm days.

My question is when I hook up my scanner, I'm checking the different parameters. So Its 60 degrees out and car is in garage. Intake temp says 70 degrees which makes since. But coolant temp says 81 degrees. I start the car and within a minute the coolant temp goes up 90 a second later goes 108..... Is that normal?

Car had been sitting for 11 plus hours so should have been completely cool.
The coolant is full, system bleed.IMG_0009.PNG
 


Pretty rare to see MAF displayed in lbs/minute.

If you have the ability to monitor for and graph misfire data, I would look there to see what cylinder(s) may not be contributing during your hesitation. If you are seeing a pattern for 1 or more cylinders, focus your efforts at determining what is causing the issue. As far as your IAT and ECT, they appear to be ok but all should be checked under the same conditions as your hesitation. Duplicate the situation and problem first. Monitor your scan data during the event and record it. Most times your problem will show up in the recorded data.

Also curious as to the vacuum reading. 29.92 in of vacuum is what is referred to as "Max Achievable Vacuum" and isn't something we see in automotive vacuum readings. Typically you are looking for 15-22 inches with the needle or reading holding steady on a properly running engine.
 
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If your thermostat is working correctly your car should warm up pretty fast. Go start your car for 30 seconds then grab the exhaust manifold.
 
The fuel trims are from car being idle.


Reading, while driving at 25 mph....... temp intake 77 degrees....coolant 190 degrees..... map reading 21 inHg.....maf reading is 2.5

It only does the stumble/hesitation periodically, at take off and again at around 20 mph
 

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It says MAP, which is manifold absolute pressure. Which should also be measured in kPa.

You could easily have issues with the MAF being dirty/out of spec, old plugs/wires, weak coils, dirty fuel injectors, weak fuel pump, clogged fuel filter etc.

It could also be transmission related as well.
 


matt5112 said:
It says MAP, which is manifold absolute pressure. Which should also be measured in kPa.

You could easily have issues with the MAF being dirty/out of spec, old plugs/wires, weak coils, dirty fuel injectors, weak fuel pump, clogged fuel filter etc.

It could also be transmission related as well.
Click to expand...


That's true... I did check fuel pressure its about 45 psi. I cleaned throttle and have not been able to find any intake leaks. Tinkering with the maf wires didn't help either.


When I unplug the maf sensor (which is a fairly new aftermarket unit) it doesn't hesitate and it has better pick up.

But I know that unplugging the maf doesn't necessarily mean the maf is bad, because unplugging it masks other components that could be the problem.

In the next week I'm going to try to do a tune up, and clean sea-foam the injectors. And see what happens.
 
45 psi under what conditions?

It should be 45 PSI with 5 psi of vacuum which is half the vacuum your car should produce at idle.

Check fuel pressure with the vacuum connector off, it should be ~50.8 psi.

If unplugging the maf is generally what we consider "the maf test" which implies the MAF is bad. I agree its not an absolute, but its probable that it is at fault.

I'd suggest hitting up a junk yard and picking up a few MAFs and trying those out. Or cleaning the one you have. Better yet, warranty it.
 
45 psi at idle ..you mean check it with with vacuum to the pressure regulator off?




I thought about grabbing a few from the junkyard, but they take them off the cars and want 80 bucks a piece for them. I may buy a used ac delco maf and take the one I have back


I bout a cheaper aftermarket maf at start up it would rev up on its own for a few seconds.. and periodically hesitate/stumble.I sent it back.

I then bought a new car-done unit (Its only a few weeks old.) It helped with the start up problem but hesitates/stumbles just the same as the other unit. I will probably return it and get a used ac delco and hope it works ..three's a charm right? lol


They want 80 bucks for the maf at the junkyards near me.
 
at idle it should be around 19-21 in Hg MAP, and as a result, fuel pressure should be 40-42 depending on vacuum and accuracy of gauge.

IIRC, the best way to check fuel pressure is at idle with the vacuum line off, should jump right to 50-52 psi.

That price on used MAFs is ridiculous. Do they come with year+ warranty at that price?

I believe I have two or three sets working factory MAF/IAC/TPS for this reason.
 
OK Thanks, I will use those specs and see what the pump reads.



And no they have at most 45-60 day warranties on the used mafs.

ebay has them for about 40 bucks 30 day warranty. I may get one from there.
 


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